The present invention relates to housings for electrical circuit components, and particularly to a surface-mountable housing for a magnetic reed switch unit for use in a physical security monitoring alarm system.
Physical security alarm system circuits often incorporate magnetic reed switches sensitive to the position of a magnet carried on a movable object such as a window sash or door. Such magnetic contact switches are commonly mounted in somewhat exposed locations, fastened to the surface of a doorway or window frame.
Since the door and window monitoring switches are only parts of an alarm circuit which involves other remotely located components, some means must be provided for electrical connection of the switches to the remainder of the circuit. Previously this has commonly been accomplished by connecting wires to externally located screw post terminals. When screw post terminals are used, they are typically left exposed, along with a short bared portion of the electrical conductors of the alarm circuit.
When screw post type terminals are left exposed it is possible to defeat the security system switch by unobtrusively attaching a conductor such as a paper clip to bridge the gap between the terminals. This can be avoided by covering the terminals with a plate such as the one disclosed in Holce et al, U.S. Pat. No. 4,210,888, but such a cover adds to the size of the switch unit and may therefore be undesirable.
Short lengths of wire may be provided extending from a switch housing and the like. Such leads, however, necessitate a solder joint or equivalent connection to the conductors of the alarm circuit. These joints must be covered with some sort of insulation material to protect the circuit, adding inconvenience and time to the process of installing an alarm circuit.
It is often desirable to test operation of each individual switch of such a security circuit. This requires the ability to make electrical contact with the switch leads. While such testing may be made possible by the provision of test points located accessibly in a switch unit, it is sometimes necessary to test a switch while it is in its installed location but disconnected from the alarm circuit. Use of soldered connections is relatively inconvenient when such testing is necessary.
While the magnetic reed switches used in alarm systems may be quite small themselves, the requirements for terminal connections and mounting of a switch in the proper location have previously resulted in relatively large switch units. Such large surface mounted switch units are often easily noticeable, detracting somewhat from the appearance of a building in which they are used.
Another problem with previously known switch units is that mounting such a switch unit on an uneven surface, using screws or similar fasteners extending through a fixed flange of a housing, may result in damaging the switch.
What is desired, therefore, is a small magnetic contact switch unit for inconspicuous surface mounting, which permits electrical connection of the switch into an alarm system circuit without exposing uninsulated portions of the alarm circuit conductors outside the switch housing, which is easily connected to the circuit conductors, and which permits electrical testing of the individual switch without physical removal of the switch from its mounted location as part of a security system, yet provides substantial protection of the electrical terminals against unauthorized bypassing of the switch.